<?xml version="1.0"?>
<svg xmlns="http://www.w3.org/2000/svg">
  <defs>
    <mask id="myMask">
      <svg x="25%" overflow="visible">
        <svg x="25%" overflow="visible">
          <polygon fill="white" points="-50 0 50 0 50 100 -50 100"/>
        </svg>
      </svg>
    </mask>
  </defs>
  <rect width="100%" height="100%" fill="lime"/>
  <circle cx="50%" cy="50" r="40" fill="red"/>
  <rect mask="url(#myMask)" width="100%" height="100%" fill="lime"/>
</svg>
